A new DC arc furnace hearth is disclosed by the Stenkvist application Ser. No. 15,587 filed Feb. 27, 1979 now U.S. Pat. No. 4,228,314, issued Oct. 14, 1980. This hearth is electrically conductive so that when constructed as part of a DC arc furnace, the arcing power can be transmitted via the hearth to a melt on the hearth and via an arc to an arcing electrode above the melt.
When used, for example, in a conventional DC arc furnace construction, carbon bricks are layed on an electrically conductive metal plate which can be connected to the DC arc power, the plate and carbon brickwork embracing an extended area. Possibly with a graphite layer layed on the carbon bricks, the usual electrically non-conductive granular refractory compound is installed. Steel rods are then driven down through this compound so as to engage the carbon brickwork or penetrate the graphite layer if used, the tops of the rods being exposed to the surface of the granular compound. Then the compound is dried and sintered as usual so that an electrically conductive hearth is formed. DC power connected to the plate on which the carbon bricks are layed is conducted via the carbon brickwork and the graphite layer if used, through the steel rods to a charge on the hearth and to the arc of an arcing electrode above the charge.
Important advantages are obtained from this hearth construction. The steel rods are installed in the form of a cluster extending substantially coextensively with the melt, and the bars can be arranged symmetrically around the arcing electrode conventionally positioned concentrically with respect to the hearth and, of course, the furnace wall. The use of a starting electrode, the requirement for a special furnace construction providing for side melt contact electrodes, and the problems of arc angularity, are all eliminated.
However, this does have one disadvantage, namely, the need for drying and sintering, or burning-in, the granular material forming the hearth surface, before it can contain the furnace melt. This procedure, required as well by all conventional hearth constructions, has always involved environmental problems, has been known to weaken the refractory furnace wall, particularly when it is of monolithic construction, and sometimes damages the integrity of the hearth itself.
The object of the present invention is to continue to enjoy the advantages of this Stenkvist application hearth while at the same time eliminating the need for the drying and sintering of the granular compound layer.